The invention relates to an automatically coupling fan for the cooling system of automobiles, comprising a thermostat formed by a gas-tight container with a rigid and a flexible wall, which thermostat contains a liquid whose steam pressure, in a preset temperature range, couples the fan to the drive shaft of the motor by way of a friction clutch.
Automobiles with combustion engines require fans to be positioned in the cooling system in order to remove heat in all driving conditions.
If the fan is rigidly connected to the motor--and in consideration of the fact that the expense in terms of fan performance quite considerable--measures are justified to reduce this expense.
In order to avoid the indicated disadvantages the prior art has long known a connection between the fan and the motor employing friction clutches or liquid slip clutches. Also employed is a fan drive with a separate electric motor, for those drive motors installed in a direction diagonal to the direction of travel. However, these designs are only partially satisfactory or are not at all satisfactory--since they are burdened with technical and operational disadvantages and disadvantages relating to cost.
An automobile fan of the type indicated at the outset is known to the prior art from DE-PS 26 35 896. In this fan the thermostat is at rest. Its coupling action is dependent on the temperature of the cooling air passing above it; the fan is coupled to the motor drive shaft within a critical temperature range as a function of the steam pressure of the boiling filler located inside of the thermostat. Coupling is performed by its flexible wall. The thermostat then runs along with the blades of the fan. The contact pressure between the thermostat and the matching fan clutch is reinforced by the centrifugal force of the liquid remaining in the thermostat.
The problem of the invention is to specify a design whose embodiment is particularly simple and cost-effective and which enables the fan to be controlled by the temperature of flow of either the cooling water or the cooling air.
This problem is solved by the invention, as indicated in the primary invention claim, in that the thermostat is configured as a metal bellows which rotates jointly with the shaft of the cooling water circulating pump, and the bellows dimensions are such that the water ring arising with the centrifugal forces exerted on the thermostat filler during rotation of the thermostat remains largely outside of the effective bellows cross-section, and in that the fan is coupled almost exclusively by the steam pressure of the filler arising within the thermostat in the predetermined temperature range; or in that--as specified in the secondary claim--the thermostat is configured as a metal bellows which rotates jointly with the shaft of the cooling water circulating pump, and the filler volume of the liquid medium within the thermostat is such that the water ring arising with the centrifugal forces exerted on the filler during rotation of the thermostat along with the shaft of the circulating pump remains largely outside of the effective cross-section of the metal bellows and in that the fan is coupled almost exclusively by the steam pressure arising within the thermostat in the predetermined temperature range.
Metal bellows manufacturers can provide the specialist with necessary information on the use of metal bellows and on the pressure that can be transmitted to the flexible wall of the metal bellows; likewise the effective bellows cross-section, as determined by the inner and outer diameters of the bellows. From this information it is possible to determine the effective quantity of filler needed for a given bellows--so as to thereby assure that the quantity of liquid filler will not cause centrifugal forces of such magnitude, in any of the operating phases, that the fan will be prematurely coupled to the circulating pump shaft.
However, the specialist can also determine the quantity of filler demanded by the pressure forces required for coupling--in order to achieve the necessary steam pressure within the predetermined temperature range, given a specific bellows volume. Bellows that meet the invention requirements can be identified from these magnitudes and from the measurement and data tables drawn up by bellows manufacturers.
In actual practice, the control of fan coupling as a function of the cooling water temperature is preferred; in previous designs, however, this has been possible only with a relatively high additional expense.